Abstract A void volume, which is measured by helium expansion tests and used in the calculation of methane adsorption amounts, is always overestimated due to helium adsorption. In this study, by comparing void volumes of carbon nanopores determined under different temperatures and pressures using GCMC (Grand Canonical Monte Carlo) simulation, suitable experimental conditions for helium expansion tests are obtained. Five volumes, including one apparent volume Vapp, three referred volumes Vref and one physical volume Vphy, are recognized. The apparent volume Vapp corresponds to the volume directly determined under traditional experimental conditions, while three referred volumes are determined at 500 K with different pressure ranges (low, moderate, high). The physical volume is calculated by multiplying a pore width and a surface area. Besides, a volume determined by using a helium probe is named an accessible volume Vacc and used as a criterion for a determined volume through mass balance. It is found that use of a void volume determined under traditional experimental conditions or a physical volume leads to negative adsorption amounts at high pressures. Considering an economic effect and measurement accuracy, determining a void volume by helium expansion tests within a moderate pressure range at 500 K is suggested. Excess isotherms of methane calculated by the suggested volume are more appropriate and of great physical meanings for further investigation of adsorption mechanisms.

中文翻译：

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碳纳米孔中氦吸附对表观空隙体积和过量甲烷吸附等温线的影响

摘要 用氦膨胀试验测量并用于计算甲烷吸附量的空隙体积，总是由于氦吸附而被高估。在这项研究中，通过比较使用 GCMC（Grand Canonical Monte Carlo）模拟在不同温度和压力下确定的碳纳米孔的空隙体积，获得了适合氦膨胀测试的实验条件。识别出五个体积，包括一个表观体积 Vapp、三个参考体积 Vref 和一个物理体积 Vphy。表观体积 Vapp 对应于在传统实验条件下直接确定的体积，而三个参考体积是在 500 K 下确定的，具有不同的压力范围（低、中、高）。通过将孔宽度和表面积相乘来计算物理体积。除了，使用氦探针确定的体积称为可接近体积 Vacc，并用作通过质量平衡确定体积的标准。发现使用在传统实验条件下确定的空隙体积或物理体积导致高压下的负吸附量。考虑到经济效果和测量精度，建议在 500 K 的中等压力范围内通过氦膨胀测试确定空隙体积。通过建议体积计算的过量甲烷等温线更合适，对进一步研究吸附机制具有重要的物理意义。发现使用在传统实验条件下确定的空隙体积或物理体积导致高压下的负吸附量。考虑到经济效果和测量精度，建议在 500 K 的中等压力范围内通过氦膨胀测试确定空隙体积。通过建议体积计算的过量甲烷等温线更合适，对进一步研究吸附机制具有重要的物理意义。发现使用在传统实验条件下确定的空隙体积或物理体积导致高压下的负吸附量。考虑到经济效果和测量精度，建议在 500 K 的中等压力范围内通过氦膨胀测试确定空隙体积。通过建议体积计算的过量甲烷等温线更合适，对进一步研究吸附机制具有重要的物理意义。